This invention relates to a new and improved chemical analysis photometer, and more particularly to such a photometer having an improved cuvette structure that provides for a zero reading of the reagent prior to mixture of a reagent and a sample.
The term "photometric" as used herein should not be considered in a restrictive sense as it is intended to be generic to the terms "colorimetric", "fluorometric" and "spectrometric". Also, the term "photometer" as used herein should not be considered in a restrictive sense and includes but is not limited to those devices sometimes referred to in the art as "colorimeters", "fluorometers" and "spectrometers". The term "light" as used herein includes radiant energy in both the visible and invisible spectrums as well as radiant energy restricted to specific wave lengths. Thus, this invention should be understood to encompass systems which utilize different types of radiation to accomplish the measurement desired. The terms "above", "below", "inward" and "outward" are used herein when viewing the drawings in a conventional manner.
An example of a prior art photometer is described and illustrated in U.S. Pat. No. 3,555,284, entitled "Multistation, Single Station Channel Analytical Photometer and Method of Use." In particular, this patent teaches a photometer that passes light through a reaction or mixing chamber which is disposed radially from separate reagent and sample chambers. Upon rotation, the sample and the reagent move under centrifical force to the reaction chamber whereupon light is passed through the reaction chamber to obtain a reading. Since the reagent and sample are mixed either before or simultaneously with the light reading, there is no way to obtain a reagent blank reading or a zero reading as the term is sometimes used herein. Thus, a reagent blank reading must be assumed. The term "obtain a reading" as used herein refers to the measurement of light transmitted through a solution in the reaction chamber of the cuvette. More particularly and as a general rule, a spectrophotometric measurement is made of the light that passes through the solution in the reaction chamber. However, light readings can be taken throughout the electromagnetic spectrum. The term "light reading" herein refers to the measurement of electromagnetic energy transmitted through the solution.
Another prior art photometer is described and illustrated in U.S. Pat. No. 3,586,484 entitled "Multistation Analytical Photometer and Method of Use." The structure of this invention is substantially the same as that of the '284 patent above. The reagent and sample are both initially placed in separate chambers, and upon rotation they mix in a third chamber. The resulting mixture is passed through a series of passageways and intermediate chambers before being deposited in a sampling chamber for analysis by light rays. Thus, there is no means of obtaining a reagent blank reading and one must be assumed. Also, it is necessary to either calibrate each cuvette to each other or to a reference because of the potential difference of the walls of each cuvette in transmitting light or to take readings to compensate for the optical transmitting difference between each cuvette, or to manufacture each cuvette so that the optical transmitting characteristic of all cuvettes is equal. U.S. Pat. No. 3,681,029 entitled "Sample Holder and Transferring Device for a Centrifuge" is very similar to the photometer of the '284 patent, and has the same disadvantage.
Yet another prior art device is described and illustrated in U.S. Pat. No. 3,873,217 entitled "Simplified Rotor for Fast Analyzer of Rotary Cuvette Type." The apparatus of this patent includes inner reagent chambers and outer sample chambers. Upon rotation, the reagent is moved to the outer sample chamber by centrifical force for mixture thereof. The light rays are passed through the sample or mixture chambers for analysis. Accordingly, it may be appreciated that a reagent blank reading may not be obtained, but must again be assumed, because the sample and not the reagent is placed in the reaction chamber and this patent has the additional disadvantage noted above for the '284 patent.
A more recent prior art apparatus is described in U.S. Pat. No. 3,811,780 entitled "Chemical Analysis Cuvette." This apparatus is capable of allowing for a reagent blank reading since the light rays are passed through the reaction chamber containing the reagent prior to mixture with a sample. However, this is a complicated apparatus, and as designed does not use centrifical force of the carousel for mixing but instead for stepping from one chamber to the next such that a syringe may be employed for transferring the sample (backed by the reagent) into a reaction chamber. Thus, as designed, this apparatus also mixes the reagent and the sample before the light rays are passed through the reaction chamber for analysis. Accordingly, a reagent blank reading must again be assumed and this patent has the additional disadvantage as noted above for the '284 patent.
Furthermore, the prior art systems require the use of a reagent blank solution separate from the test solution to obtain blank reading. Thus, at least two aliquots of reagent are required.